In the communications industry, cables which connect central offices with distribution centers in subscriber loops generally include a plurality of pairs of individually insulated condutors. Each pair of the conductors is twisted together. While the twist in any pair is commonly unidirectional, present day techniques include a so-called S-Z twist in which the direction of twist is reversed periodically.
A pair of insulated conductors having a unidirectional twist are twisted together in a well-known apparatus. That apparatus includes two supply reels mounted inside a surface of revolution which is generated by a flier bow that is caused to be revolved about the supply reels. As the conductors are payed off the supply reels and fed upwardly through the bow, they become associated together as a twisted pair. The twisted pair of conductors is advanced over sheaves and then through a multi-grooved capstan whereafter it is taken up in a reel that is positioned outside the cone of revolution of the bow.
In a cable manufacturing plant, it is not uncommon to have a large number of twisting apparatus which are arranged in rows having aisles therebetween. typically, one factory operator is assigned to a plurality of twisting apparatus with each of the plurality requiring attention, such as reel handling, at staggered times.
For one reason or another, conductor breaks occur and present problems for the operator. It is obviously advantageous to detect conductor breaks as soon as possible to eliminate wasted machine time and to avoid the pass-through of only one conductor from one of the supply reels to the take up reel. Also, since the tension on strand material which passes through the twisting apparatus is estalished for a pair of conductors, the absence of one conductor causes excessive elongation in the other and renders it unuseable for communication purposes.
In order to detect conductor breaks early on, twisters as they are called in the art, have been equipped with proximity sensors. These sensors have been used by setting the sensitivity to distinguish between the presence of one or two conductor elements which are advanced past the sensor. Unfortunately, the metallic content between one and two conductors, especially in the finer gauge sizes is so insubstantial that precise settings on the sensors are required.
The problem of broken strand detection has been addressed by the prior art, In U.S. Pat. No. 3,999,695, for example, a running filament is passed over a counterweighted cylinder in a manner to cause the cylinder to rotate. Breakage of the filament allows the cylinder to return to a position where it blocks the flow of a fluid from an orifice and causes a measuraanble change in the fluid pressure.
The prior art includes somewhat elaborate arrangements for improving the sensitivity of sensors used for detecting cross-sectional deviations in moving elongated material. In U.S. Pat. No. 4,136,454, laminar material is moved between two rollers, one of which is supported for movement away from the other. A sensor is spaced from the one roller and generates signals in response to displacements of the one roller caused by thickness variations in the laminar material. See also U.S. pat. No. 4,232,447.
What the prior art lacks is an uncomplicated detection apparatus which is particularly suited to detect a missing conductor of a twisted pair. As such, it must be easily integrated with the conventional twister, must be inexpensive, and must be capable of providing a visual indication to an operator.